鋼筋混凝土圓形橫箍筋橋柱遲滯行為之實驗研究

Abstract

前人為能良好評估橋柱之勁度折減、強度衰減、束縮效應以及路徑相依特性等行為，提出一套新型的耐震評估方法：容量位移雙反應譜，此方法改良之前的各種遲滯模型進而使用新平滑遲滯模型，此模型能良好模擬出不同設計參數的橋柱受到不同特性的震源下的行為，同時將橋柱轉換為單自由度系統後進行非線性動力歷時分析，將其分析結果進行參數分析，建立容量位移雙反應譜，此反應譜可以同時針對不同的橋柱設計參數建構出相對應之非彈性位移譜及損傷指數反應譜，兩者可以更好的評估橋柱的耐震行為。 經前人之分析與探討，容量位移雙反應譜在矩形柱和圓柱皆可以準確地預測出橋柱的遲滯行為，其中損傷指數經過實驗證明能有效的判斷橋柱破壞狀況，在現有橋梁結構中能更加的準確、快速的分析其耐震性能，在評估橋柱的損傷程度以及強度上更加直觀。 容量位移雙反應譜目前的數據庫仍然需要增加，在實務設計中有不同斷面及配置的橋柱，除了矩形與圓形螺箍筋，還有圓形圓箍筋形式的設計，為盡可能地涵蓋上述設計範圍，需要設計一系列的試體進行實驗，本研究參考前人矩形與圓形螺箍筋的實驗安排，使用圓形圓箍筋的配置形式設計五座涵蓋實務設計範圍的縮尺RC橋柱，進行反覆側推載重試驗，設計參數包含縱向鋼筋比與高寬比，為兩種主要會影響混凝土強度的參數。 試驗完成後，針對實驗得到的結果觀察橋柱的破壞情形，包括裂縫產生、主筋斷裂情形、箍筋圍束行為進行探討，藉由致動器及應變計得到的數據繪製遲滯迴圈，計算其位移分布，同時與前人所做的矩形RC柱進行結果對比，相互比較其中差異性，探討不同配置下的橋柱行為。

In the past, an innovative seismic design and evaluation method for reinforced concrete bridges was proposed to effectively evaluate the degradation of stiffness, strength deterioration, pinching effect, and path dependence properties of the columns. This method, known as the capacity based inelastic displacement spectra, integrates various types of hysteresis models to better simulate the nonlinear behavior. The model precisely simulates the behavior of reinforced concrete columns under different earthquake characteristics with various designed parameters. It achieves this by conducting a series of nonlinear time history analyses of single-degree-of-freedom (SDOF) systems simplified from the true columns to analyze the results. Through establishing these spectra, the inelastic displacement spectra associated with corresponding damage indices for RC columns can be constructed, allowing for a better evaluation of seismic performance. According to the analysis and investigation from previous research, the capacity based inelastic displacement spectra can accurately predict the hysteresis behavior of the RC columns, both in rectangular and circular cross section. The damage index, which has been experimentally validated, can effectively assess the state of damage in bridge columns. In existing bridges, this method enables a more precise and rapid analysis of their seismic performance and provides a more intuitive evaluation of the extent of damage and strength in RC bridge columns. The current data base for capacity based inelastic displacement spectra still need to be expanded. In practical design, columns come in different cross sections and configurations. Besides rectangular and circular spiral hoop, there are also designs with circular hoops. To satisfy a variety of designs, a series of specimens need to be designed and tested. In this study, referencing the experimental arrangements used for rectangular and circular spiral hoops by previous researchers, five scaled-down RC bridge columns were designed with circular hoops to encompass the practical design range. These columns were then subjected to cyclic loading test. The design parameters included longitudinal reinforcement ratios and aspect ratios, as these are the two main factors that influence the strength of concrete. After completing the tests, the damage pattern was observed and investigated, including the formation of the cracks, fracture of the longitudinal reinforcement, and the confinement behavior of hoops. By analyzing the data obtained from actuators and strain gauges to plot the hysteresis loops and calculate the displacement distributions. Additionally, these results were compared with those from previous study on rectangular RC columns to identify differences and gain a better understanding of column behavior under different configurations.